In data storage systems, write performance is increased by utilizing well known data caching techniques, including write back caching. When a storage controller receives a write request from a host computer, the storage controller stores the write data in the write cache, if space is available in the write cache, and notifies the host computer that the write request is complete. This then frees up the host computer to issue additional read or write requests. If write cache space is not available, the storage controller must instead transfer the write request directly to the slower storage devices, thus degrading write performance.
Once the write data is in the write cache, the storage controller institutes various policies to determine when, which, and how much write data to transfer to destination storage devices. The actions surrounding this transfer are referred to as destaging data from the write cache. Destaging write data is important as it frees up write cache space to accept new write requests from host computers, and the data is stored on storage devices in redundant RAID configurations. Redundant RAID configurations preserve data in the event of a single storage device failure—and in some RAID configurations—multiple storage device failures. It is therefore desirable to efficiently destage write data from a storage controller write cache to storage devices.